ExperienceLife and style'I had been prepared to fight the enemy in Iraq, but I never expected to feel betrayed by my own people'

I had always had great respect for soldiers. My father was a Vietnam veteran. I was amazed by his tenacity, so much so that I wanted to follow his example, to do something significant and fight on the frontline. I joined the army in 2004, and a year later I was sent to Iraq.

The biggest shock, once I'd finished my training, was meeting the enemy – seeing what you're up against and realising they're kids your age. The most profound thing was thinking that if I had grown up on that continent, I could have been one of those guys.

I remember the first person I killed. He was about my age, 22. We were in a town south-west of Baghdad, on patrol; we started to get shot at and we retaliated.

When someone tries to take your life, it's more intimate than the strongest love; more intense than the strongest fear or even joy. It's the most extreme emotion you have ever felt. He was trying to kill me and I did not hesitate to kill him first.

People don't die how they do in movies. It's not a quick shot to the chest and they drop. Unless you hit somebody in a particular point above the eyes, they will not die right away, and we don't train for head shots – they're too hard and unreliable. Instead, I shot him 12 or 15 times until he dropped. It took around two and a half seconds, then I moved on. Hesitation will get you killed.

Once we had made sure the area was safe, it was our duty to provide medical aid to wounded enemy forces as well as to our own. The man I had shot was still alive. I will never forget the way he looked. He was surprised and sobbing a bit in disbelief. I think he must have thought his God was going to protect him and destroy me instead. He died while we were trying to save him. I didn't find out his name.

At that moment – and this may sound naive – I realised that nobody wakes up and thinks they are the bad guy. The man who had died fighting against me that day would have got up every morning thinking he was the righteous one.

That day changed everything for me. Now I knew the scariest thing in the dark is us. Him, me – it's all the same. I was his nightmare; he was mine – both evil in each other's eyes.

Eventually, I became a whistleblower. I had expected to fight in combat, but not the sort of battle I took on. I was talking to another soldier and he said, "You know what else is messed up? You remember that family that got murdered back in March?"

He filled me in on the details of what later became known as the Mahmudiyah killings. "That was us, man," he said. "That was Green" – referring to Steven Green [now serving life imprisonment for rape and murder]. I couldn't believe what I was hearing. In one sentence he had dismantled for me every good thing we'd done, every hospital we'd built, every school we'd protected. I had been prepared to fight the enemy, but I never expected to feel betrayed by my own people.

A group of them had broken into the family's house, raped the 14-year-old girl, shot them all, then tried to cover it up. I did my own research and spoke to two other soldiers who'd been on checkpoint the day the family was murdered. One confirmed all the details.

I now had a confession and I knew I had to turn them in. But how? I told the unit outside my chain of command, assuming they'd get me out, but it didn't work: they thought I was lying. They threatened to charge me with making false statements and perjury, and they interrogated me. By this time I had realised there was no evidence – it was just my word against that of the five soldiers involved – but I stuck to my guns and didn't budge.

Eventually one of the men cracked during interrogation and confessed that, while he'd had no part in the rape and murders, he had been there and had covered it up. The story broke – and everybody knew that I was telling the truth.

After they were sentenced, I got death threats. Some people called me a traitor, but others thought I was a hero: I had risked my life to expose the culprits.

After coming home and getting out, I am more confused than ever about what happened. It's been hard but I'm OK. I rent a house in Salt Lake City. I have a girlfriend. I worry about paying the bills, and I live a normal life.

As told to Aqib Khan

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